Take Marlin's figures for most things with a pinch of salt!
Remember the actual measured weight of the car can be considerably less than the quoted axle design weights and maximum gross weight (which are used by the brake system calculations at SVA to govern acceptable brake effort).
I ended up with an unladen weight on the SVA scales (we'll assume Marlin are quoting without fluids or fuel!) of about 720kg for the Type-R car. I reckon if I was a complete weight nazi during the build, and didn't fit various options (additional panelling etc) I could probably have got the Type-R car down to about 680kg, which probably means the smaller K-series builds could achieve about 630kg, realistically.
Rich (Bigrich) has built a pretty stripped-out K-series version. What was your measured weight at SVA Rich?